The present invention relates to a method and system for measuring an inherent characteristic of a planarization process. In particular, the invention relates to a method and system of measuring a threshold length utilizing a blanket wafer.
Many steps in the manufacture of semiconductor devices result in a highly irregular surface on the semiconductor wafer substrate. In order to improve the manufacturability of the devices on the wafer, the surface is ordinarily planarized between processing steps.
A common method of planarization is often referred to as chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d). CMP is an important improvement in planarization technology because it allows for planarization across larger portions of the wafer. Because this planarization extends across a substantial portion of the wafer, CMP allows for xe2x80x9cglobal planarizationxe2x80x9d as well as xe2x80x9clocal planarization.xe2x80x9d
While CMP techniques have provided substantial improvements in the quality of global planarization, researchers continue to seek new advancements and adjustments to existing processes in order to provide as high a quality of planarization as possible. The concept of xe2x80x9cplanarization length,xe2x80x9d first described by Dennis Okuma Ouma of M.I.T. in a thesis entitled xe2x80x9cModeling of Chemical Mechanical Polishing for Dielectric Planarization,xe2x80x9d is one way in which the quality of a system""s global planarization can be evaluated, characterized, and compared.
A known method for measuring planarization length includes measurement of an oxide thickness on a polished patterned wafer utilizing a pattern density mask, and then calculating the planarization length from the measured data. The problem with this method is that the use of patterned wafers requires significant processing time and cost for the patterning steps, or requires purchasing of the density mask. Furthermore, the use of the pattern density mask leads to a complicated data analysis.
Accordingly, there is a need in the art for a simplified method for characterizing a planarization process that saves processing time and is cost efficient.
The present invention provides a method and system for measuring a new characteristic, defined below as the threshold length, of a planarization process.
In one aspect of the invention, a method is provided for determining the threshold length of a planarization process. The method includes measuring a varying thickness of a film layer on a portion of a blanket wafer, and then calculating the threshold length based upon variations in the thickness of the portion of the blanket wafer.
In another aspect of the invention, a method is provided for characterizing a planarization process. The method includes determining the threshold length of the planarization process using a blanket wafer.
In another aspect of the invention, a method is provided for comparing two or more planarization processes. The method includes determining the threshold length of a first planarization process using a blanket wafer, determining the threshold length of a second planarization process using a blanket wafer, and then comparing the threshold length of the first planarization process to the threshold length of the second planarization process.
In another aspect of the invention, a method for is provided for determining whether a planarization process is effective to planarize a wafer. The method includes calculating the threshold length of the planarization process, and comparing one or more feature lengths of a wafer to the calculated threshold length to determine whether the planarization process would be effective to planarize the wafer.
In another aspect of the invention, a method is provided for comparing two or more planarization processes characterized by different parameters. The method includes determining the threshold length of a first planarization process using a blanket wafer, determining the planarization length of a second planarization process using a patterned wafer, and then comparing the threshold length of the first planarization process to the planarization length of the second planarization process.
In yet another aspect of the invention, a system is provided for measuring the threshold length of a planarization process. The system includes a blanket wafer thickness determinator adapted to measure a varying thickness of a film layer of a blanket wafer and to create a signal indicative of said varying thickness, and a threshold length calculator in communication with the blanket wafer thickness determinator and adapted to calculate a threshold length based upon said signal received from said blanket wafer thickness determinator.